In the field of cosmetic, personal care, and pharmaceutical products emollients are usually defined as an agent that softens or smooths the skin and which tend to reduce the roughness, cracking and irritation of the skin. The ancient Greek physician, Galen, is thought to have made one of the first emollients consisting of beeswax, spermaceti, almond oil, borax and rosewater.
At the present, there are numerous ingredients which function as emollients in a wide variety of products, and which ingredients may act in subtly different ways. For example, certain emollients sit on the surface of the skin and serve to impede water loss from the skin. Such ingredients are generally comprise large molecules that forms a hydrophobic barrier to help prevent water from leaving the surface of the skin. Examples of such emollients are silicone derivatives and petroleum jelly.
Other ingredients that have been used as emollients include a number of fatty acids derived from either plants or animal sources. Fatty acids generally comprise aliphatic hydrocarbon or other organic chains with carboxylic substituents on them, typically having between 8 and 24 carbon atoms in the chain backbone. Fatty acids are often used in creams, lotions, shaving creams, lipsticks and as pressing agents in pressed powders and blushes. Fatty acids which are used in cosmetics formulations generally include at least stearic acid, oleic acid, myristic acid and palmitic acid. Other typical fatty acids include linoleic acid, behenic acid, and other common fatty acids of the general formula C.sub.n H.sub.2n+1 COOH.
Fatty alcohols are also used as emollients. They are said to be less sticky and less heavy than many other fatty materials, such as the fatty acids, and are frequently used to improve the viscosity and stability of lotions and creams. They also have utility in reactive hair dying and perming products. Examples of fatty alcohols which find use in the field of cosmetics and personal care products are cetyl alcohol, lauryl alcohol, stearyl alcohol and oleyl alcohol, and others of the general formula C.sub.n H.sub.2n+1 OH.
Additional examples of emollients are fatty esters. One of the best qualities of fatty esters is that they do not feel as oily to the touch as some other types of emollient fatty ingredients. Examples include isopropyl palmitate, isopropyl myristate and glyceryl stearate.
An important emollient is jojoba oil which is derived from the seed of the species Simmondsia chinensis. It is a plant derived oil with excellent skin feel which is composed almost exclusively of wax esters, with little or no triglycerides present. A major portion of the production of jojoba oil is used by the cosmetic industry as an emollient in a variety of products. Although jojoba oil has long been used as an emollient, some difficulty has been found in forming stable emulsions using the oil.
The synthesis of esters and waxy esters of natural oils is known, as disclosed in U.S. Pat. Nos. 4,031,019 and 4,152,278 (the "Bell" patents), and this technology may be traced back to earlier seminal work done in U.S. Pat. No. 1,944,887. In the Bell patents, wax esters are prepared from acids obtained from hydrogenated vegetable oils. Fatty alcohols are esterified with the fatty acids to yield the wax esters which are described as useful for lubricants in replacement of sperm oil. U.S. Pat. No. 1,944,887 describes the manufacture of esters from monobasic saturated fatty acids containing 6 to 13 carbon atoms with aliphatic monohydric alcohols containing from 12 to eighteen carbon atoms.